You may discard up to 2 Energy from your Benched Pokmon
You cant lose speed and opponent's can not remove your speed unless a card specifically says so , as is the case with Spikeshell Harrier, which references the blue shells from the Mario Kart franchise
Of course, if you can use the mana better, you can change the symmetric effect to your advantage, and theres a chance there were decks that could do just this
For example, classic Food Chain combos only rely on you being able to cast creature spells and activate mana abilities, neither of which are commonly locked out by prison effects
The crown jewel is Charizard VMAX Shiny (#308), worth approximately 40,000 ($284)
Beyond potentially reviving past archetypes, Mox Opal was a key part of the once-infamous Krak-Clan Ironworks combo